The present invention relates to upgrading coal by removing sodium ions. More particularly, the invention relates to removing sodium ions from coal by means of water-washing and ion-exchange.
The presence of large amounts of sodium in coal is undesirable as it contributes to fouling of combustion facilities. The fouling problems can arise if sodium exceeds about 3%w (as Na.sub.2 O), yet several important deposits of coal contain more than that much sodium. Thus, a process which can economically remove, for example, 30 to 50 percent of the sodium, can be very desirable and can be a prerequisite condition for exploitation of sizeable deposits.
The levels of sodium oxide in the ash at which coal combustion can lead to fouling problems are not yet clearly defined, and can be different for different coals. Nevertheless, levels in excess of about 3%w are not desirable and coals with more than 4%w in the ash, are generally difficult to market. Some Powder River Basin coal samples have been found to yield over 6%w of sodium oxide.